1. Field of the Invention
The present invention relates to an ignition coil, which is used for generating a spark between a pair of electrodes in a spark plug, in an internal-combustion engine such as a vehicular engine.
2. Description of Related Art
In an ignition coil used in a vehicular engine, for example, a control command from an electronic control unit (ECU) of the engine is transmitted to an igniter having a control circuit for controlling a switching element, and an electric current is passed and cut off through a primary coil of the ignition coil using the igniter.
In the case where the igniter is incorporated in a case of the ignition coil, particularly, in the igniter, a semiconductor integrated chip is packaged in the form of a flip chip on a ceramic substrate, in which a conducting portion constituting the control circuit and the like are formed, and the ceramic substrate is bonded on a lead frame. In the semiconductor integrated chip, an integrated circuit employing a junction isolation method is formed. The ignition coil using such an igniter is disclosed in JP2004-6506A corresponding to U.S. Pat. No. 7,084,729, for example.
In the igniter using the ceramic substrate, when the ceramic substrate and the semiconductor integrated chip are on a coil-side relative to the lead frame, the semiconductor integrated chip is exposed to a high electric field of the coil. In such a case, a silicon substrate surface (P-SUB region on a silicon substrate side) of the semiconductor integrated chip disposed on the coil-side is connected to GND. Thus, the silicon substrate surface is located between the high electric field of the coil and a circuit surface of the semiconductor integrated chip, so that the high electric field hardly has a bad influence on the circuit surface.
A configuration of the igniter using the ceramic substrate is complex and creates rising costs. Accordingly, it is proposed that the ceramic substrate is not used and the semiconductor integrated chip is directly mounted on the lead frame. In this case, the silicon substrate surface of the semiconductor integrated chip is bonded to the lead frame, and circuit elements in the semiconductor integrated chip are connected to each other by wire bonding.
However, in the case where the ceramic substrate is not used, when the circuit surface of the semiconductor integrated chip is disposed facing the coil-side, [the circuit surface is exposed to the high electric field. As a result, a parasitic transistor is generated in the integrated circuit in the semiconductor integrated chip, and thereby malfunctions such as latch-up may occur.